Drew Hammill, a top aide to Pelosi, said the unidentified staff member was fully vaccinated and did not have recent contact with the top California Democrat, though the speaker's office is taking extra precautions as a result.
"Yesterday, a fully vaccinated senior spokesperson in the speaker’s press office tested positive for COVID after contact with members of the Texas state legislature last week," Hammill said in a statement obtained by Fox News.
"This individual has had no contact with the speaker since exposure. The entire press office is working remotely today with the exception of individuals who have had no exposure to the individual or have had a recent negative test. Our office will continue to follow the guidance of the Office of Attending Physician closely."
On Tuesday, Pelosi and her staff were spotted wearing masks again at the Capitol. Following a loosening of mask restrictions by the Capitol physician, many members have opted against masks in recent weeks.
Asked about her covid-positive staffer Tuesday, Pelosi said: "I'm sorry he has it. All the more reason for all of us to be vaccinated as he was. Wear a mask. Take every precaution."
She said any decision to bring masks back full-time to the House of Representatives "will be up to the Capitol physician."
Separately, Axios first reported that a White House official also tested positive for coronavirus after attending the same rooftop reception in Washington as the Pelosi staffer last Wednesday night. The White House aide was also fully vaccinated and experienced mild symptoms.
A White House official confirmed to Fox News the staffer tested COVID-19 positive on Monday outside White House grounds and has remained off site, awaiting a confirmatory PCR test. The White House medical unit conducted contact tracing and determined the staffer had "no close contacts among White House principals and staff."
"We know that there will be breakthrough cases, but as this instance shows, cases in vaccinated individuals are typically mild," a White House official told Fox News. "The White House is prepared for breakthrough cases with regular testing. This is another reminder of the efficacy of the COVID-19 vaccines against severe illness or hospitalization. We wish our colleague a speedy recovery."
The news of the breakthrough cases come after six members of the Texas delegation tested positive for the virus after leaving the state Capitol and coming to Washington last week in an attempt to thwart a special legislative session where Republicans seek to pass new election reforms.
"I think the vice president’s office put out that she was tested and there was no detection of COVID-19," Psaki said. "They also put out some specific details about their proximity to the individuals who tested positive as well. We take these precautions incredibly seriously and abide by the guidance of our help and medical experts."
Fox News' Erin McEwan, Kelly Phares and Thomas Barrabi contributed to this report.